CN106257013B

CN106257013B - Method and system for boost control

Info

Publication number: CN106257013B
Application number: CN201610397162.2A
Authority: CN
Inventors: H-R·欧萨乐; 肖柏韬; A·N·班克
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2015-06-16
Filing date: 2016-06-07
Publication date: 2020-03-31
Anticipated expiration: 2036-06-07
Also published as: CN106257013A; RU2016122171A3; RU2016122171A; DE102016109791A1; US9677481B2; US20160369716A1; RU2719775C2

Abstract

The invention relates to a method and a system for boost control. A method for improving boost pressure control in a boosted engine system is provided. In one example, an air bypass coupled across an intake compressor of an engine system may be held open for a predetermined time during tip-in. Keeping the air bypass open during tip-in enables the compressor to spin faster, and this faster speed can be translated into achieving the desired higher boost when the air bypass is subsequently closed in less time than was previously possible.

Description

Method and system for boost control

Technical Field

The present application relates to a method for adjusting compressor recirculation valve events to improve boost control.

Background

The engine system may be configured with a boosting device, such as a turbocharger or supercharger, for providing a charge of charge air and increasing peak power output. In a turbocharged engine, air flow (and therefore torque) to the engine may be regulated by the action of a throttle located at the engine intake. Boost pressure may be adjusted by the action of an exhaust gas bypass or Wastegate (WG) coupled across the exhaust turbine and an air bypass or Compressor Recirculation Valve (CRV) coupled across the intake compressor. By controlling the flow of exhaust gas over the turbine, the exhaust bypass can regulate boost pressure (and thus power delivered to the compressor), and the air bypass can be used generally for compressor surge management.

Typically during tip-in, where increased torque is required, the exhaust bypass is fully closed and the air bypass is also fully closed, providing increased power to the turbocharger, for example as shown in US20140260241 to Jankovic et al. When the torque demand is high, the air delivered to the engine is increased by immediately closing both the exhaust bypass and the air bypass, thereby increasing the power delivered to the turbocharger. Therefore, the boost pressure is accumulated.

Disclosure of Invention

However, the present inventors have recognized methods to further increase boost response and reduce turbo lag. In one example, boost pressure may be increased by a method comprising: opening an air bypass around an air compressor supplying air to the engine in response to an operator demand for additional torque from the engine (e.g., during tip-in); and keeping the air bypass open for a predetermined time and then closing the air bypass.

As one example, an air bypass may be opened in response to the additional torque demand being greater than a threshold. During a predetermined time when the air bypass is open, boost pressure may not build, but the compressor may rotate faster. In addition, when the air bypass is initially opened, the turbine speed may rise at a faster rate. At the end of the predetermined time, when the air bypass is closed, then the increased compressor speed transitions to reach the desired boost level in less time than was previously possible. In this way, turbo lag is reduced. Once the boost pressure reaches the target threshold, the throttle, exhaust bypass, and air bypass may be actively controlled to maintain boost at the desired threshold. Overall, supercharged engine performance is improved and turbocharger lag may be reduced.

It should be appreciated that the summary above is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

Drawings

FIG. 1 shows a schematic diagram of an example boosted engine system.

FIG. 2 shows a high level flow chart for opening the air bypass for a predetermined time during tip-in.

FIG. 3 illustrates a high level flow chart for adjusting the exhaust bypass and the air bypass based on a difference between an actual air charge and a desired air charge.

FIG. 4 illustrates example coordination of an exhaust bypass, an air bypass, and an intake throttle adjustment to provide a desired boost pressure according to the present disclosure.

Detailed Description

The following description relates to systems and methods for improving boost pressure control in a boosted engine system, such as the system of FIG. 1. During tip-in, when the operator requested torque demand is high, the controller may be configured to execute a routine, such as the routine of fig. 2, to open (or remain open) an air bypass coupled across an intake compressor of the engine system for a predetermined time. Keeping the air bypass open during tip-in enables the compressor to spin faster. Once the predetermined time has elapsed, the air bypass may be closed, which further translates high compressor speeds into high boost levels. The controller may further execute a routine, such as the routine of FIG. 3, to adaptively adjust each of the exhaust bypass, the air bypass, and the intake throttle coupled across the exhaust turbine to maintain boost at a desired level. An example adjustment is shown in fig. 4. In this way, higher boost levels may be achieved.

FIG. 1 shows a schematic diagram of an example turbocharging system 100, which includes a multi-cylinder internal combustion engine 10 and two

turbochargers

120 and 130. As one non-limiting example, the engine system 100 can be included as part of a propulsion system for a passenger vehicle. The engine system 100 is capable of receiving intake air via an intake air channel 140. The intake duct 140 can include an air filter 156. The engine system 100 may be a split engine system in which the intake duct 140 is branched into a first and a second flat traveling gas duct downstream of the air filter 156, each of which includes a turbocharger compressor. In the resulting configuration, at least a portion of the intake air is directed to the compressor 122 of the turbocharger 120 through a first parallel intake duct 142, and at least another portion of the intake air is directed to the compressor 132 of the turbocharger 130 through a second parallel intake duct 144 of the intake duct 140.

A first portion of the total intake air compressed by the compressor 122 may be supplied to the intake manifold 160 through the first parallel branch intake passage 146. Thus,

intake air channels

142 and 146 form a first parallel branch of the air intake system of the engine. Similarly, a second portion of the total intake air can be compressed by the compressor 132, where it can be supplied to the intake manifold 160 through the second parallel branch intake passage 148. Thus,

intake passages

144 and 148 form a second parallel branch of the air intake system of the engine. As shown in FIG. 1, intake air from

intake ports

146 and 148 can be recombined through common intake port 149, where the intake air can be provided to the engine, before reaching intake manifold 160.

In some examples, intake manifold 160 may include an intake manifold pressure sensor 182 for estimating manifold pressure (MAP) and/or an intake manifold temperature sensor 183 for estimating manifold air temperature (MCT), both of which may be in communication with controller 12. The intake 149 may include an air cooler 154 (which may also be referred to as a heat exchanger) and an intake throttle 158. The position of intake throttle 158 can be adjusted by control system 50 via a throttle actuator (not shown) communicatively coupled to controller 12.

The compressor recirculation passage 150 may be provided for throttle tip-in, torque control, control of condensate formation in the charge air cooler, and compressor control following compressor surge control. For example, to reduce compressor surge, such as when the driver releases the accelerator pedal, boost pressure may be bled from the intake manifold, downstream of the air cooler 154, and upstream of the intake throttle 158 to the intake port 140 (specifically, downstream of the air filter 156 and upstream of the junction of the intake ports 142 and 144). By flowing charge air from upstream of the intake throttle inlet to upstream of the compressor inlet, the boost pressure may be rapidly reduced, thereby expediting boost control. By adjusting the position of an air bypass or compressor recirculation valve (also referred to as a compressor surge valve) 152 positioned therein, the flow through the compressor recirculation passage 150 can be adjusted. In some embodiments, the air bypass 152 may be configured as a two-way valve that is adjustable to one of a fully closed position and a fully open position. In other embodiments, the air bypass 152 may be a continuously variable valve whose position can be adjusted to a fully open position, a fully closed position, or any position therebetween. Accordingly, the air bypass 152 may also be referred to herein as a continuously variable compressor recirculation valve, or CCRV. In the depicted example, the air bypass 152 is configured as a throttle valve, although in other embodiments, the air bypass may be configured differently (e.g., as a poppet valve). It should be appreciated that although the air bypass is shown configured for use with the V-6 twin turbocharged engine of FIG. 1, the air bypass may be similarly applied in other engine configurations, such as to I-3, I-4, V-8, and other engine configurations having one or more turbochargers. In an alternative configuration, compressor recirculation passage 150 may be positioned such that flow travels from upstream of air cooler 154 to a location upstream of

compressors

120 and 130. In another configuration, there may be two recirculation paths, each with an air bypass, each positioned such that flow travels from the compressor outlet to the compressor inlet.

Engine 10 may include a plurality of cylinders 14. In the depicted example, engine 10 includes six cylinders arranged in a V-type configuration. Specifically, the six cylinders are arranged in two

groups

13 and 15, wherein each group includes three cylinders. In alternative examples, engine 10 can include two or more cylinders, such as 4, 5, 8, 10, or more cylinders. These various cylinders can be equally divided or arranged in alternative configurations such as V-type, inline or cartridge type, and the like. Each cylinder 14 may be configured with a fuel injector 166. In the depicted example, fuel injector 166 is a direct in-cylinder injector. However, in other examples, fuel injector 166 can be configured as a port-based fuel injector.

Intake air supplied to each cylinder 14 (also referred to herein as a combustion chamber 14) via a common intake passage 149 may be used for fuel combustion, and the products of combustion may then be exhausted via a cylinder bank-specific parallel exhaust passage. In the depicted example, a first group 13 of cylinders of engine 10 may be capable of exhausting combustion products through a first parallel exhaust passage 17, and a second group 15 of cylinders may be capable of exhausting combustion products through a second parallel exhaust passage 19. Each of the first and second parallel exhaust passages 17 and 19 may further include a turbocharger turbine. Specifically, the combustion products exhausted through the exhaust passage 17 can be directed through an exhaust turbine 124 of the turbocharger 120, which in turn can provide mechanical work to the compressor 122 via a shaft 126 to provide compression for the intake air. Alternatively, some or all of the exhaust gas flowing through the exhaust passage 17 can bypass the turbine 124 through a turbine bypass passage 123, which is controlled by an exhaust gas bypass or wastegate 128. Similarly, the products of combustion exhausted through exhaust passage 19 can be directed through an exhaust turbine 134 of turbocharger 130, which in turn can provide mechanical work to compressor 132 via a shaft 136 to provide compression of intake air flowing through a second branch of the engine's intake system. Alternatively, some or all of the exhaust gas flowing through the exhaust passage 19 can bypass the turbine 134 via a turbine bypass passage 133, which is controlled by an exhaust gas bypass or wastegate 138.

In some examples,

exhaust turbines

124 and 134 may be configured as variable geometry turbines, wherein controller 12 may adjust the position of the turbine blades (or vanes) to vary the level of energy obtained from the exhaust flow and applied to their respective compressors. Alternatively,

exhaust turbines

124 and 134 may be configured as variable nozzle turbines, wherein controller 12 may adjust the position of the turbine nozzle to vary the level of energy obtained from the exhaust flow and applied to their respective compressors. For example, control system 50 can be configured to independently vary the vane or nozzle positions of

exhaust turbines

124 and 134 via their respective actuators.

During tip-in, where increased torque is required, typically the exhaust bypasses 128, 138 may be closed, while the throttle 158 may be fully opened, and the air bypass 152 may be fully closed. Together, these actions ensure that increased air is delivered to the engine and that the power delivered to the turbocharger is increased. Thus, boost pressure may build up slowly until it reaches a target set point. However, the inventors have identified potential use of an air bypass valve to further increase boost response. Specifically, during tip-in, by keeping the air bypass valve initially open for a predetermined time (as shown in FIG. 2), the compressor speed, and therefore, the turbocharger speed, may be increased as explained below.

The compressor power balance equation is given as follows

(1)

(2)

Where Ht is turbine enthalpy, Hc is compressor enthalpy, N_tcIs the turbine speed, w_cIs the compressor air flow, C_p,cIs the specific heat capacity at a constant pressure,

is the temperature at the inlet of the compressor,

is the compressor outlet pressure (boost),

is compressor inlet pressure, gamma_cIs specific heat ratio, η_cIs the compressor efficiency of isentropic. The specific values of these parameters depend on the engine and the operating conditions of the engine.

During tip-in, when the air bypass is held open, the pressure ratio remains nearly close to 1 (i.e.,

) Hc is therefore a negligible term. Therefore, the temperature of the molten metal is controlled,

(3)

and therefore the turbine speed rises at a faster rate than when the air bypass is closed.

Once the turbocharger speed reaches a threshold speed (or a threshold time has elapsed), the air bypass may be closed. By closing the air bypass, increased turbocharger speed may be translated into higher boost levels. In this way, it is possible to reach a higher boost level in a shorter time. Once the boost pressure reaches the target threshold, the throttle, exhaust bypass, and air bypass may be actively controlled to maintain the boost at the desired threshold, as shown in FIG. 3.

An exhaust bypass or wastegate actuator regulates boost pressure by controlling the flow of exhaust gas over the turbine at the corresponding point. However, exhaust bypass actuation generally has a slower effect on boost pressure than air bypass actuation due to slower turbocharger power. Specifically, to change boost pressure, the exhaust bypass first needs to accelerate the turbine and compressor (since they are connected on the same shaft). The controller controls exhaust bypass action through feed forward and feedback components. The feed-forward component is responsive to a desired (reference) boost pressure and operating conditions, while the feedback component is responsive to a difference between an actual (measured or estimated) boost pressure and the desired boost pressure. The opening of the exhaust bypass is adjusted in response to a feedback adjustment of the boost pressure adjustment error to obtain an accurate steady state boost pressure adjustment in the presence of uncertainty and external disturbances. However, any action of the air bypass and the intake throttle (which also has a substantially immediate effect on boost pressure) can confound exhaust bypass control that is not fast enough to counteract the effect of the compressor recirculation valve or the intake throttle.

During nominal engine operating conditions, the air bypass 152 may be held nominally closed or nearly closed. In this position, the valve may be operating with a known or negligible leakage. Then, in response to surge, the opening of the air bypass 152 may be increased. In some embodiments, one or more sensors may be coupled in the compressor recirculation passage 150 to determine the mass of the recirculated flow delivered from the throttle inlet to the intake. The various sensors may include, for example, pressure, temperature, and/or flow sensors. Additionally, by coordinating the operation of the air bypass with the operation of the exhaust bypass, boost response and surge spacing may be increased.

The hot boosted air (charge air) from

compressors

122 and 132 enters the inlet of air cooler 154 (also referred to as a Compressed Air Cooler (CAC) or heat exchanger), cools as it travels through the air cooler, and then exits to pass through throttle 158 and then into engine intake manifold 160. Ambient air flowing from outside the vehicle may enter engine 10 through the front end of the vehicle and traverse the air cooler, thereby helping to cool the boosted air. Condensate may form and accumulate in the air cooler as the ambient air temperature decreases, or during humid or rainy weather conditions, where the boosted air is cooled below the water dew point temperature. Further, when the boosted air entering the air cooler is boosted (e.g., boost pressure and/or air cooler pressure greater than atmospheric pressure), condensate may form if the air cooler temperature falls below the dew point temperature. Further, if condensate accumulates in the air cooler, the condensate may be ingested by the engine during periods of increased airflow. Thus, unstable combustion and/or engine misfire may occur.

Prior to throttle 158, the intake pressure may be measured at the outlet of the air cooler. As such, the intake pressure may be referred to as the pre-throttle pressure. In one example, the suction pressure may be determined via a sensor, such as sensor 232. The ratio between the suction pressure and the atmospheric pressure may be referred to as the suction pressure ratio. The ratio between the air cooler pressure (which may be the suction pressure or the average CAC pressure) and the atmospheric pressure may be referred to as the air cooler pressure ratio. When the air cooler pressure ratio and/or the suction pressure ratio is greater than 1, the suction pressure is greater than atmospheric pressure, and the engine is operating under boosted conditions. Thus, when the suction pressure ratio is greater than 1, condensate may form in the air cooler. However, if the suction pressure ratio is kept below 1 or 1, no condensate may form. In this way, reducing the suction pressure ratio from above 1 to below 1 or 1 may reduce air cooler condensate formation.

Exhaust gas in the first parallel exhaust passage 17 may be directed to the atmosphere through the branched parallel exhaust passage 170, while exhaust gas in the second parallel exhaust passage 19 may be directed to the atmosphere through the branched parallel exhaust passage 180.

Exhaust passages

170 and 180 may include one or more exhaust aftertreatment devices, such as catalysts and one or more exhaust gas sensors.

In some embodiments, engine 10 may further include one or more Exhaust Gas Recirculation (EGR) passages for recirculating at least a portion of the exhaust gas from first and second parallel exhaust passages 17, 19 and/or first and second parallel-branched

exhaust passages

170, 180 to first and second

parallel intake passages

142, 144 and/or parallel

branched intake passages

146, 148 or intake manifold 160. These may include a high-pressure EGR loop for providing high-pressure EGR (HP-EGR) and a low-pressure EGR loop for providing low-pressure EGR (LP-EGR). When included, HP-EGR may be provided in the absence of boost provided by

turbochargers

120, 130, while LP-EGR may be provided in the presence of turbocharger boost and/or when exhaust gas temperatures are above a threshold. In other examples, both HP-EGR and LP-EGR may be provided simultaneously. The low-pressure EGR loop may recirculate at least some exhaust gas from each of the branched parallel exhaust passages downstream of the exhaust turbine to a corresponding parallel intake passage upstream of the compressor. Each of the LP-EGR loops may have a corresponding LP-EGR valve for controlling exhaust gas flowing through the LP-EGR loop, and a respective charge air cooler for reducing the temperature of exhaust gas recirculated to the engine intake. The high pressure EGR loop may recirculate at least some exhaust gas from each of the parallel exhaust passages upstream of the exhaust turbine to a corresponding parallel intake passage downstream of the compressor. EGR flow through the HP-EGR loop may be controlled via respective HP-EGR valves and HP-EGR charge air coolers.

The position of the intake and exhaust valves of each cylinder 14 may be adjusted by hydraulically actuated lifters coupled to valve pushrods, or by a cam profile switching mechanism in which cam lobes are used. In this example, at least the intake valve in each cylinder 14 may be controlled by cam actuation using a cam actuation system. Specifically, intake valve cam actuation system 25 may include one or more cams and may utilize variable cam timing or lift for the intake and/or exhaust valves. In an alternative embodiment, the intake valves may be controlled by electric valve actuation. Similarly, the exhaust valves may be controlled by a cam actuation system or by electric valve actuation.

Engine system 100 may be controlled at least partially by a control system 50 including controller 12, and by input from a vehicle operator via an input device (not shown). The control system 50 is shown receiving information from a plurality of sensors 16 (various examples of which are described herein) and sending control signals to a plurality of actuators 81. As one example, the sensors 16 may include a humidity sensor, a MAP sensor 182, and an MCT sensor 183. In some examples, common intake passage 149 may include a Throttle Inlet Pressure (TIP) sensor 232 for estimating throttle inlet pressure, also referred to as boost pressure, and/or a throttle inlet temperature sensor for estimating throttle air temperature (TCT). In other examples, one or more of the EGR passages may include a pressure sensor, a temperature sensor, and an air-to-fuel ratio sensor for determining EGR flow characteristics. As another example, actuators 81 may include fuel injector 166, HP-

EGR valves

210 and 220, LP-EGR valve (not shown), throttle 158, and

wastegates

128, 138. Other actuators, such as various additional valves and throttles, may be coupled to various locations in the engine system 100. The controller 12 receives signals from the various sensors of FIG. 1 and employs the various actuators of FIG. 1 to adjust engine operation based on the received signals and instructions stored on a memory of the controller.

FIG. 2 illustrates an example method 200 of opening an air bypass for a predetermined time during tip-in. Specifically, when sufficient torque is required, the air bypass may not be immediately closed, but may be delayed to close, thereby increasing boost. Based on instructions stored on a memory of the controller, and in conjunction with signals received from sensors of the engine system, such as the sensors described above with reference to fig. 1, a controller, such as controller 12 of fig. 1, may execute instructions for performing method 200 and the remaining methods included herein (e.g., method 300). The controller may employ an engine actuator of the engine system, such as the actuator of FIG. 1, to adjust engine operation according to the method described below.

At 202, the routine includes estimating and/or measuring engine operating conditions. These include, for example, pedal position, torque demand, boost demand, turbine speed, compressor inlet temperature, engine temperature, MAP, MAF, boost pressure, throttle inlet pressure, intake pressure, humidity, and the like. At 204, the method includes determining whether there is a sudden increase in torque demand (e.g., due to tip-in). For example, it may be determined whether the torque request has increased more than a threshold amount (e.g., a momentary increase in torque request) and/or whether the accelerator pedal has been depressed more than a threshold amount within a threshold time. The tip-in pedal may be a tip-in pedal from an idle condition (e.g., when the pedal is in a substantially released position), or from a steady state cruise condition (e.g., when the pedal is partially depressed).

If the torque request is greater than the threshold (or tip-in is identified), then method 200 proceeds to 208, where the torque request is converted to a desired air boost. For example, the desired boost may be based on the transmission gear and the weight of the vehicle being driven by the engine, as well as the slope of the road on which the vehicle is traveling. As an example, the desired boost may be higher when the vehicle is climbing a steep incline. However, the desired boost may be lower, for example, when the vehicle is descending a hill. The estimated conditions may be measured directly with sensors, such as, for example, a temperature sensor, a MAF sensor, a MAP sensor, a throttle inlet pressure sensor, and a pedal position sensor, and/or may be estimated based on other engine operating conditions. Engine operating conditions may include engine coolant temperature, engine oil temperature, Mass Air Flow (MAF), manifold pressure (MAP), boost (e.g., from a boost pressure sensor), engine speed, idle speed, barometric pressure, driver demanded torque, air temperature, vehicle speed, and so forth.

Method 200 then proceeds to 210 where an air bypass around the air compressor is opened (or remains open) at 210. For example, if a tip-in pedal large enough to require boost is detected and no boost or a boost level is small before the tip-in pedal, the air bypass is opened immediately. However, if the air bypass is already open prior to tip-in (e.g., for surge mitigation), then the air bypass is kept open at 210. The technical effect of opening the air bypass for a predetermined time is that the compressor rotates faster and, therefore, the turbine speed rises at a faster rate, as explained with reference to equations 1-3. In some embodiments, the air bypass or compressor recirculation valve may be configured to be two-position, wherein opening the air bypass includes adjusting the air bypass to a fully open position. However, in some other embodiments, the air bypass may be a continuously adjustable valve, wherein the air bypass may be adjusted to a position closer to the fully open position. Then, at 212, a timer is set.

At 214, the predetermined time is estimated based on engine operating conditions. For example, the predetermined time may be calibrated to allow for rapid acceleration of the compressor. For example, the predetermined time may be based on the time it takes for the turbine speed to reach a threshold speed (e.g., 60,000 rpm). As another example, the predetermined time may be a preset duration (e.g., such as 400 ms).

Method 200 then proceeds to 216 where it may be determined whether a predetermined time has elapsed at 216. For example, a predetermined time may be considered to elapse when a preset duration (as determined by a timer) expires. As another example, when turbine speed reaches a threshold, it may be considered that a predetermined time has elapsed and the method proceeds to 220 where the air bypass may be closed. However, if the predetermined time has not elapsed while checking at 216, the method proceeds to 218 where the air bypass is held open until the predetermined time has elapsed at 218. This initial opening of the air bypass may reduce the initial accumulated boost. However, once the predetermined time has elapsed, the method proceeds to 220 where the air bypass is closed at 220. When the air bypass is configured as a two-position valve, closing the air bypass includes adjusting the air bypass to a fully closed position. However, when the air bypass includes a continuously variable valve position, closing the air bypass includes adjusting the air bypass to a position closer to the fully closed position. The technical effect of delaying the closing of the air bypass is that faster turbocharger speeds translate to higher boost levels. In this way, boost may be quickly built up and the time to torque may be reduced by delaying closing of the air bypass.

Returning to 204 of the method, when checking at 204, if the torque demand is below the threshold, the method proceeds to 206, where the air bypass is closed without any delay. When the torque demand is below the threshold, the time to reach torque may be increased by closing the air bypass without any delay. After closing the air bypass, the method proceeds to 222 where the actual air boost may be calculated at 222. Actual boost levels achieved may be directly measured via sensors such as, for example, a temperature sensor, a MAF sensor, a MAP sensor, a throttle inlet pressure sensor, and a pedal position sensor, and/or conditions may be estimated based on other engine operating conditions. Engine operating conditions may include engine coolant temperature, engine oil temperature, Mass Air Flow (MAF), manifold pressure (MAP), boost (e.g., from a boost pressure sensor), engine speed, idle speed, barometric pressure, driver demanded torque, air temperature, vehicle speed, and so forth. Next, method 200 may then proceed to 224 where the exhaust gas bypass and the air bypass may be controlled based on the difference between the actual air charge and the desired air charge at 224, as explained in FIG. 3.

Thus, an example method includes opening an air bypass around an air compressor supplying air to the engine in response to an operator demand for additional torque from the engine, and keeping the air bypass open for a predetermined time, and then closing the air bypass. The air bypass may be opened in response to the additional torque demand being greater than a threshold. Further, keeping the air bypass open and closed may occur while operator demand continues to exist. The predetermined time may be calibrated to allow rapid acceleration of the compressor while achieving additional torque after shutdown. The compressor may be driven by a turbine coupled to an exhaust of the engine. The operator demand may be translated into a desired air boost from the compressor. The method further includes controlling an exhaust bypass around the turbine to control air boost pressure from the compressor, the controlling responsive to a difference between a desired air boost pressure and an actual air boost pressure (shown in FIG. 3). The method further includes controlling the air bypass after a predetermined time in response to a difference between the desired air charge and the actual air charge, as explained in fig. 3.

Turning now to FIG. 3, an example method 300 for adjusting an exhaust bypass and an air bypass based on a difference between an actual air charge and a desired air charge is shown. Specifically, after the initial tip-in, when the air bypass is closed after a delay, the opening of each of the exhaust bypass, the air bypass, and the throttle may be adaptively adjusted based on engine operating conditions.

At 302, a boost error may be determined. Thus, the boost error may be the difference between the actual air boost and the desired air boost. After an initial tip-in, when the air bypass is closed after a delay, faster turbocharger speed may translate into reaching higher boost levels in less time than prior methods. Actual boost levels achieved may be directly measured via sensors such as, for example, a temperature sensor, a MAF sensor, a MAP sensor, a throttle inlet pressure sensor, and a pedal position sensor, and/or conditions may be estimated based on other engine operating conditions. Engine operating conditions may include engine coolant temperature, engine oil temperature, Mass Air Flow (MAF), manifold pressure (MAP), boost (e.g., from a boost pressure sensor), engine speed, idle speed, barometric pressure, driver demanded torque, air temperature, vehicle speed, and so forth. Once the actual boost pressure is determined, a boost pressure error may be calculated by subtracting the desired boost pressure from the actual boost pressure (as determined at 208 of method 200). Based on the boost error, the exhaust bypass may be adjusted. In this way, the exhaust bypass regulates boost pressure by controlling the gas flow over the turbine, and thus the power delivered to the compressor. Any adjustments to the exhaust bypass result in a change in boost pressure, but the boost pressure change occurs relatively slowly due to turbocharger inertia.

Method 300 proceeds to 304 where it is determined whether the boost error is greater than a threshold (e.g., zero) at 304. If the boost error is greater than the threshold, indicating that the actual air boost is greater than the desired air boost, then method 300 proceeds to 308 where the exhaust bypass opening may be increased at 308. By increasing the exhaust bypass opening (or feedback adjusting the exhaust bypass), the exhaust manifold pressure and turbine inlet pressure are reduced, thereby reducing turbine speed, and therefore turbine power.

However, if the boost error is below the threshold when checked at 304, the method proceeds to 306 where the exhaust bypass opening may be reduced at 306. By reducing the exhaust bypass opening, the exhaust manifold pressure and turbine inlet pressure are increased. This increases turbine speed and, therefore, turbine power.

In some embodiments, the exhaust bypass opening may be adjusted based on a desired air charge (feed-forward adjustment). For example, if a higher air boost is desired, the exhaust bypass may be closed (or adjusted to a more closed position). For example, the exhaust bypass may be opened (or adjusted to a more open position) when the desired air boost decreases. In this way, the exhaust bypass may be adjusted based on the desired air boost. In addition to feed-forward adjustments to the exhaust bypass, boost errors may be determined, and as explained previously, the exhaust bypass may then be adjusted based on the boost errors (feedback adjustments).

After feedback adjustment of the exhaust bypass at 306 and 308, the method proceeds to 310 where it may be determined whether the compressor is near or at a surge limit at 310. In this way, the effect of opening or closing the air bypass on boost pressure is substantially immediate, thus allowing boost and surge control. Compressor surge is an undesirable condition that can occur when a high compressor speed at a given time results in more air being compressed than the engine can intake. Compressor operation in the surge region results in unacceptable NVH, and possible degradation of engine performance. At 310, method 300 includes determining whether a turbocharger compressor operating point is near or at a surge limit. For example, a controller (e.g., controller 12 of FIG. 1) may make the determination based on sensed parameter values, such as turbocharger shaft speed, inlet and outlet pressures of the compressor, compressor flow rate, and so forth. For example, the compressor may be determined to be at or about the surge limit when the ratio of the outlet pressure and the inlet pressure of the compressor is greater than a threshold (e.g., 2). If at 310 it is determined that the compressor is near or at the surge limit, then method 300 proceeds to 316 where the air bypass opening may be increased (feed forward adjustment of the air bypass). Thus, by increasing the opening of the air bypass, compressor operation can be moved out of the hard/soft surge region. In doing so, surge is immediately reduced and supercharged engine performance is improved. However, continuously recirculating the air around the compressor can cause fuel economy losses when additional compressor work must be built up through the additional turbine work. Increased turbine work generally results in higher exhaust pressures and increased engine pumping work. The method proceeds to 318 where each of the exhaust bypass, the air bypass, and the throttle may be adaptively adjusted to maintain engine operation at 318.

For example, the exhaust bypass may be closed when the desired boost pressure increases. By closing the exhaust bypass, exhaust manifold pressure and turbine inlet pressure are increased. This increases the turbine speed and thus the turbine power. After closing the exhaust bypass, the exhaust bypass may be further adjusted to maintain boost based on an error between the actual boost pressure and the desired boost pressure. Based on the surge limit, and further based on the boost error, the air bypass may be further adjusted, as explained previously. For example, as the boost error increases, the air bypass opening may be decreased to increase the boost pressure while the air bypass opening may be increased to decrease the boost pressure. In this way, since the effect of the air bypass adjustment on boost pressure is substantially immediate, a faster and more accurate regulation of boost pressure is achieved by using an air bypass adjustment that is consistent with the exhaust bypass.

The intake throttle may be further adjusted to achieve a desired manifold air flow rate. As such, as the torque request increases, the desired manifold air flow rate may be based on the driver torque request with an increase in air flow rate. For example, when the actual or estimated manifold air flow caused by the exhaust bypass and the air bypass adjustment becomes lower than the desired air flow rate, the intake throttle opening may be increased to compensate for the error and increase the manifold air flow. As another example, when the actual or estimated manifold air flow caused by the exhaust bypass and the air bypass adjustment becomes higher than the desired air flow rate, the intake throttle opening may be decreased to compensate for the error and reduce the manifold air flow. In another example, the intake throttle is directly actuated in response to an actual boost pressure measurement (TIP sensor) that is itself responsive to exhaust and air bypass adjustments. In this way, the throttle is adjusted to reduce the error between the desired airflow rate (based on the operator torque request) and the actual boost pressure (caused by the exhaust bypass and air bypass adjustments). Thus, in this way, by adaptively adjusting each of the exhaust bypass, the air bypass, and the intake throttle, a desired boost may be maintained.

Returning to 310, when checked at 310, if the compressor is not near or at a surge limit, the method proceeds to 312, where it is determined whether a condensate forming condition exists in the condenser. In one example, the condensate forming condition includes when the suction pressure (e.g., pressure at the outlet of the air cooler, upstream of the throttle) is greater than a threshold pressure, which may be a first threshold pressure. In one example, the threshold pressure may be atmospheric pressure. In another example, the threshold pressure may be a pressure greater than atmospheric pressure. Alternatively or additionally, the controller may determine the suction pressure ratio as a ratio between the suction pressure and the atmospheric pressure. Thus, the condensate forming conditions may include when the suction pressure ratio is greater than 1. In another example, the condensate forming condition includes when the humidity is greater than a first threshold. The humidity may be a measured or inferred humidity. For example, the humidity may be one or more of a measured ambient humidity and/or intake air humidity. In an alternative example, humidity may be inferred based on windshield wiper on/off conditions or duty cycle. The first threshold may be based on a humidity level at which condensate may form in the air cooler (also referred to as a heat exchanger).

Returning to 312, if a condensate forming condition exists, the method proceeds to 316 where the air bypass opening may be increased. Increasing the opening of the air bypass may reduce the suction pressure and reduce condensate forming conditions in the air cooler. The method then proceeds to 318 where each of the air bypass, exhaust bypass, and throttle may be adaptively adjusted to maintain engine operation as previously explained at 318.

However, if at 312, there is no condensate forming condition, the method continues to 314 where it may be determined whether the accelerator pedal is released at 314. In response to releasing the accelerator pedal, wherein reduced torque is required, the method proceeds to 316 where the air bypass opening may be increased. If the air bypass increases the recirculation flow to the compressor inlet, the opening is increased, and the method proceeds to 318, where each of the air bypass, the exhaust bypass, and the intake throttle may be adaptively adjusted, and the method ends. In this way, a desired level of boost may be achieved, and engine operation may be maintained.

In one example, a method is provided that includes opening an air bypass around an air compressor that supplies air to an air intake of an engine for a predetermined time in response to an operator actuated tip-in of an accelerator pedal, and controlling the air bypass based on an error between a desired air boost and an actual air boost provided by the compressor after the predetermined time, the desired boost based in part on a position of the accelerator pedal. In this way, faster turbocharger speeds may be translated into higher boost levels in less time than in prior approaches. In this example, increasing the air bypass may additionally or alternatively be in response to the ratio of the outlet pressure and the inlet pressure of the compressor being at, or about, a hard surge limit. In any of the foregoing examples, increasing the air bypass may additionally or alternatively be in response to an operator actuated release of an accelerator pedal. Further, the desired boost may be based on the weight of the vehicle being driven by the engine, as well as the slope of the road on which the vehicle is traveling and the transmission gear. In any of the foregoing examples, the method may additionally or alternatively comprise cooling said air supplied to the air inlet by an air cooler or heat exchanger. In any of the foregoing examples, the method may additionally or alternatively comprise increasing the air bypass when a condensate forming condition is present in the heat exchanger. In any of the foregoing examples, the condensate forming conditions may include one or more of the following: the pressure at the air inlet is greater than atmospheric pressure; or the humidity of the ambient air is greater than a threshold value.

Accordingly, by adaptively adjusting each of the exhaust bypass, the air bypass, and the throttle, engine operation may be maintained. Turning now to FIG. 4, an example coordinated adjustment of the exhaust bypass, air bypass, and intake throttle is shown. The combination allows for rapid and accurate boost pressure control, especially during tip-in. FIG. 4 shows the change in boost pressure at curves 402 and 404, which relate to the operator torque request at curve 416, the intake throttle (manifold) air flow at curve 406, the exhaust bypass or wastegate opening at curve 408, and the air bypass or compressor recirculation valve opening at

curves

410 and 412. In each case, adjustments to each of the air bypass, exhaust bypass, and throttle are shown as adjustments to a two-position valve, which may be adjusted to one of a fully closed position and a fully open position. However, in other embodiments, adjustments may be made to the continuously variable valve, the position of which can be adjusted to a fully open position, a fully closed position, or any position therebetween. In each case, the boost pressure achieved with the delayed closing of the air bypass is shown as a solid line (at curves 402 and 410), and the boost pressure without delay is shown as a dashed line (at curves 404 and 412). The torque demand threshold is shown at curve 414. All plots of engine operation over time are shown along the X-axis.

Prior to t1, the engine may be operated at a boost level (curve 402, solid line) below threshold 414. Specifically, the desired boost level may be relatively low, and thus the engine may be operated with the air bypass closed, the exhaust bypass open, and the throttle closed.

At t1, for example, in response to tip-in, the torque request may be greater than a threshold (curve 414), as indicated at curve 416. When a tip-in is detected to be large enough to require a boost, and before the tip-in, the boost is not initiated or the boost level is small (such as less than 1inHg, for example), the air bypass may be opened as soon as the tip-in is detected (note that if the air bypass is opened before the tip-in, for example, for surge mitigation, it will remain open), as shown by curve 410. Further, the exhaust bypass is closed (curve 408) and the throttle is opened (curve 406). As shown at curve 402, the initial opening of the air bypass may reduce the initial boost accumulation. However, this opening of the air bypass will allow the turbine to rotate faster than if the air bypass were closed (or maintained closed). After a predetermined time has elapsed (e.g., between t1 and t 2), the air bypass is closed, as shown at curve 410. For example, the predetermined time may be based on a time at which the estimated turbine speed reaches a threshold. At t2, the air bypass is closed, causing the system to quickly establish boost and improve the time to torque as shown by curve 402 between times t2 and t 3.

If the air bypass is immediately closed at t1, as shown by dashed line 412, the initial boost pressure may be higher, as shown at curve 404, but the rate of rise of boost pressure (curve 404) may be slower than when the air bypass is closed with a delay (curve 402).

At t3, the torque demand drops below the threshold (414), as shown at curve 416. Between t3 and t4, when the torque demand is decreasing (e.g., accelerator pedal released), the air bypass, exhaust bypass, and throttle may be actively adjusted. For example, an air bypass may be opened, and further, an exhaust bypass may be opened, and a throttle may be closed. Opening the combination of both the air bypass and the exhaust bypass allows the boost pressure to drop rapidly (curve 402).

At t4, the torque request may begin to increase. During the time between t4 and t5, the air bypass may be closed and the exhaust bypass may be maintained open. Further, the throttle may be open. By opening the air bypass when the exhaust bypass is closed, more compressed air may be directed to the engine intake, increasing boost pressure, as shown at curve 402. Further, the air bypass, exhaust bypass, and throttle may be actively adjusted based on an error between the desired air charge and the actual air charge, the compressor being at or near a surge limit, and further based on condensate forming conditions in the air cooler. Thus, by adaptively adjusting each of the air bypass, exhaust bypass, and throttle, boost pressure may be maintained at a desired level. In general, supercharged engine performance is improved, providing fuel economy benefits.

After a significant amount of time has elapsed, at time t6, the torque demand is shown at curve 416. At time t6, the air bypass is open (curve 410), the exhaust bypass is also open (curve 408), and the throttle is open (curve 406). Prior to t7, the desired boost level may be relatively low, as shown at curve 416.

At t7, for example, the torque demand may increase, as shown at curve 416. However, at t8, the torque demand is below the threshold 414, as indicated by curve 416. The closing of the air bypass is not delayed when the driver requested torque demand is small. Thus, the air bypass is closed at t8 (curve 410). Further, the exhaust bypass and throttle may also be closed, as indicated by

curves

408 and 406, respectively. Due to the combination of exhaust bypass and air bypass adjustments, the actual boost level (curve 402) may reach the desired boost level shortly after t 8. Further, the air bypass, exhaust bypass, and throttle may be actively adjusted based on an error between the desired air charge and the actual air charge, the compressor being at or near a surge limit, and further based on condensate forming conditions in the air cooler.

In this way, adjustments to the exhaust bypass, air bypass, and throttle may deliver faster and more accurate boost. In general, supercharged engine performance is improved, providing fuel economy benefits.

In one example, a method for increasing boost is provided that includes compressing ambient air to supply compressed air to an engine air intake, thereby directly supplying ambient air to the engine air intake through a recirculation valve (air bypass) in parallel with the air compressor. In this example, in response to an operator demand for additional torque from the engine, the method may include opening the recirculation valve a calibratable time when the additional torque demand exceeds a threshold. After the calibratable time has elapsed, the method may include controlling the recirculation valve based on an error between a desired air boost and an actual air boost provided by the compressor, wherein the desired boost is based in part on an operator demand. The method may further include controlling the compressor based on an error between a desired air charge and an actual air charge provided by the compressor, and also controlling ambient air entering the air inlet and compressed air entering the air inlet via a throttle positioned proximate the air inlet, wherein the controlling may be based in part on an operator demand. The compressor may be driven by a turbine coupled to exhaust of the engine, and wherein the compressor control includes bypassing a portion of the engine exhaust around the turbine. The method further includes increasing an opening of the recirculation valve in response to a ratio of an outlet pressure to an inlet pressure of the compressor being at or about a hard surge limit. The method further includes cooling air supplied to the air inlet through the heat exchanger. The method also includes increasing a recirculation valve when a condensate forming condition is present in the heat exchanger. The method further includes a feed-forward adjustment of engine exhaust bypassing the turbine based on the desired boost pressure.

It is noted that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The control methods and programs disclosed herein may be stored as executable instructions in non-transitory memory and executed by a control system that includes a controller in combination with various sensors, actuators, and other engine hardware. The special purpose programs described herein may represent any number of processing strategies such as one or more of event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various acts, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in other cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts, operations, and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described acts, operations, and/or functions may be represented graphically in code programmed into the non-transitory memory of the computer readable storage medium in an engine control system, where the acts are performed by executing instructions in a system that includes various engine hardware components in combination with an electronic controller.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above techniques can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. It is to be understood that such claims are intended to cover combinations of one or more of such elements, neither requiring nor excluding two or more of such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

Claims

1. A method for an engine, comprising:

opening an air bypass around an air compressor that supplies air to an air inlet of the engine for a predetermined time in response to an operator-actuated tip-in of an accelerator pedal; and

after the predetermined time, increasing the air bypass in response to a ratio of an outlet pressure to an inlet pressure of the compressor being at or near a hard surge limit based on an error between a desired air boost and an actual air boost provided by the compressor, the desired boost based in part on the position of the accelerator pedal.

2. The method of claim 1, further comprising increasing the air bypass in response to operator actuated release of an accelerator pedal of the accelerator pedal.

3. The method of claim 1, wherein the desired boost pressure is further based on a weight of a vehicle driven by the engine and a slope of a road on which the vehicle is traveling.

4. The method of claim 1, further comprising cooling the air supplied to the air inlet by a heat exchanger.

5. The method of claim 4, further comprising increasing the air bypass when condensate forming conditions are present in the heat exchanger.

6. The method of claim 5, wherein the condensate forming conditions comprise one or more of: the pressure at the air inlet is greater than atmospheric pressure; or the humidity of the ambient air is greater than a threshold value.

7. A method for an engine, comprising:

compressing ambient air to supply compressed air to an engine air intake;

supplying ambient air directly to the engine air inlet through a recirculation valve in parallel with an air compressor;

opening the recirculation valve for a calibratable time when the additional torque demand exceeds a threshold in response to an operator demand for additional torque from the engine;

after the calibratable time, controlling the recirculation valve based on an error between a desired air boost and an actual air boost provided by the compressor, the desired boost based in part on the operator demand, wherein the compressor is driven by a turbine coupled to an exhaust of the engine, and wherein the compressor control comprises bypassing a portion of the engine exhaust around the turbine;

controlling the compressor based on the error between a desired air charge and an actual air charge provided by the compressor; and

the ambient air entering the air inlet and the compressed air entering the air inlet are also controlled by a throttle positioned proximate the air inlet, the control based in part on the operator demand.

8. The method of claim 7, further comprising increasing an opening of the recirculation valve in response to a ratio of an outlet pressure to an inlet pressure of the compressor being at or near a hard surge limit.

9. The method of claim 7, further comprising cooling the air supplied to the air inlet by a heat exchanger.

10. The method of claim 9, further comprising increasing the recirculation valve when condensate forming conditions are present in the heat exchanger.

11. The method of claim 7, further comprising a feed-forward adjustment of the engine exhaust bypassing the turbine based on the desired boost pressure.